Unlocking Hidden Sands: Seismic Interpretation Strategies for Thin Challenging Sand Deposit

This paper presents seismic challenges in unlocking a previously unrecognized shallow thin sandstone reservoir in the Shammar Formation, deposited directly above base Cenozoic/Cretaceous unconformity. Although penetrated by wells targeting deeper Formations, it remained unidentified due to limited data and lack of geological focus. Dense seismic interpretation coupled with well data integration and drilling results, revealed thin, small sand basins in fault-bounded, leading to unlocking new opportunities and maturing additional hydrocarbon volumes. Fine-tuned seismic interpretation of the unconformity carried out using different band-pass frequency filters, relative acoustic impedance and variance attributes from poststack seismic data. This approach supported stratigraphic analysis and helped in building a conceptual model of thin sand deposits at sub-seismic resolution. Flattening the seismic cube at the top of the Tertiary helped analyze reflection patterns within an incised valley. Natih topography influenced channelized sediment flow, creating favorable conditions of pathway for sand accommodation in fault-bounded spaces within a Tertiary rift setting. Despite limited well data, seismic indications of sand continuity were validated through limited electrical logs and mud logs. Two wells were selected for recompletion; a high water cut producer, and an inactive water injector. Both intersected the shallow sand at geologically promising locations based on the seismic depositional model, and were perforated in the newly identified sand unit. They produced at good oil rates, confirming bypassed pay and validating the model. A performance difference between the wells aligned with predicted reservoir quality trends, supporting confidence in seismic interpretation. The results supported planning the first horizontal well in this reservoir unit and prompted two more perforations to appraise sand in a different structural setting. This eliminated the need for costly appraisal wells, resulting in significant CAPEX savings and showcasing the value of integrating seismic interpretation with selective recompletion of underutilized wells. By targeting existing assets and applying a robust geological model, production was successfully enhanced from concept to execution. This work introduces a unique workflow combining advanced seismic interpretation with practical well screening using limited mud log data correlated with washed-out logs. The novelty lies in identifying previously unrecognized stratigraphic targets and maturing reservoir potential cost-effectively without drilling new dedicated wells.